The present invention relates to a high elongation and high stretch-recovery synthetic fiber suitable for preparing clothing free from stuffiness and excellent in comfort, more particularly to a high elongation and high stretch-recovery synthetic fiber suitably used for a clothing such as an inner wear, a hosiery, an intermediate a sport wear, or the like, having such as polyurethane type synthetic fiber excellent in moisture absorbing/releasing property, wet fastness to rubbing and strength-retaining ratio under wet conditions, a method for producing the same and a fabric using such a fiber.
It is well-known that the wearing comfort of clothing is improved by using a synthetic fiber imparted with a moisture absorbing property, a water-absorbing property, a moisture releasing property, a moisture permeability or others so that the discomfort due to sweat in the clothing is mitigated. When clothing such as inner-wear, a hosiery, intermediate wear, sportswear or others is worn in direct contact with, or close to, human skin, it is possible to impart the clothing with a function for promptly releasing sweat out of the clothing by applying this prior art, whereby cool clothing free from stuffiness and a clinging feel, even if the wearer sweats, is obtainable.
Attempts for imparting synthetic fibers with a moisture absorbing property, a water-absorbing property, a moisture releasing property, a moisture permeability or others have been often related to polyamide and polyester type synthetic fibers. For example, Japanese Examined Patent Publication (Kokoku) No. 60-457 discloses a composite yarn composed of a high moisture absorbent filament and a low moisture absorbent fiber, and Japanese Examined Utility Model (Kokoku) Publication No. 60-40612, Japanese Unexamined Patent Publication (Kokai) No. 60-215835 discloses knit and woven fabrics using the above-mentioned composite yarn. In Japanese Unexamined Patent Publication (Kokai) No. 2-99612, No. 4-361616, No. 4-361617, No. 9-41204, No. 9-41221 and others, synthetic fiber fabrics improved in moisture absorbing property are disclosed which use a sheath-core type composite fiber obtained by a composite spinning wherein a high moisture absorbent resin is disposed as a core around which is arranged a non- or low-moisture absorbent resin. In the above prior art, there is a disclosure in that, if a ratio of the high moisture absorbent core encircled by the low moisture absorbent sheath polyester resin becomes higher, the core resin is swollen with water when moistened or dyed to expand the sheath, whereby cracks are generated in the fiber to destroy and damage the fiber structure, resulting in the deterioration of physical properties such as a mechanical strength when the fiber is subjected to a wet treatment such as dyeing or is worn by a wearer. In the above Japanese Unexamined Patent Publication (Kokai) No. 9-41204 and No. 9-41221, a design of a sheath-core type composite fiber is disclosed wherein a polyamide inherently moisture absorbent to some extent is used as a core and a fiber cross-section is non-circular so that sweat is guided from a skin surface to a fabric due to a capillary action and then is absorbed into the moisture absorbent core resin while accelerating the release of the moisture out of the clothing. Even in this design, however, it is said that there may be the deterioration of mechanical strength during the dyeing process due to the swelling of core resin. For the above reasons, it is apparent that the sheath-core type fiber structure design is not applicable for modifying a high elongation and high stretch-recovery synthetic fiber in which the elongation of the fiber is as large as several hundreds of %.
Moisture absorbent synthetic fibers have been known, such as an acrylic type composite fiber with a salt type carboxylic group being introduced into a surface layer, a polyacrylate type fiber, a maleic anhydride type fiber, a polyvinyl alcohol type fiber, an alginate type fiber, or a polyurethane fiber, each composed of a polymer having a water absorbent group in a molecule.
Most of high elongation and high stretch-recovery synthetic fibers such as polyurethane type synthetic fiber or polyether-ester type synthetic fiber are used in the form of an elastic fabric exhibiting a high stretchability obtained by mixing the same with polyamide type synthetic fiber, polyester type synthetic fiber, regenerated cellulosic fiber, cotton, silk, wool or others. This elastic fabric is tailored to a stretchable clothing simultaneously satisfying a well-fitted feeling, a motion follow-up ability and wearing comfort. Because the stretchable clothing is designed so that the elastic fabric always fits a human body, a space between the human body and the fabric in tight contact therewith must be small. For the above reason, and based on requirements for the design of stretchable clothing, the stretchable clothing has an disadvantage in that it is liable to be stuffy to lower the comfort. Thus, there is a reason in that a high elongation and high stretch-recovery synthetic fiber must be moisture absorbable, water absorbable and moisture releasable as well as being moisture-permeable.
As a stretchable clothing which requires close contact of a human body with a fabric, an elastic fabric must have a high color fastness, for example, to rubbing caused by other clothing superposed thereon. For instance, it is said that in the superposed clothing mixedly knit or woven with natural fiber such as silk or polyamide type synthetic fiber, color staining is generally liable to occur by the frictional contact with an elastic fabric in general having an inferior color fastness in a high temperature and high humidity atmosphere because the higher the water absorption ratio of the fiber, the lower a color fastness to rubbing in a wet condition (hereinafter merely referred to a fastness to rubbing), the improvement of the color fastness of the synthetic fiber having a high elongation and a high stretchability is also desired in this respect.
A polyurethane yarn is disclosed in EP 0,892,094 A2, having a water absorption ratio in a range from 200 to 3,000% by weight (at 25xc2x0 C.) obtained by melt-spinning polyurethane containing water-soluble polyalkylene-ether-polyol having a number-average molecular weight in a range from 2,000 to 13,000 in a polymer molecule. According to Examples or others in this publication, there is a description in that this known water absorbent polyurethane fiber is poor in tensile strength when swollen. It could be said that a fiber having the water absorption ratio exceeding 200% by weight at 25xc2x0 C. and inferior in physical property when swollen is liable to absorb water during the dyeing process to cause fiber breakage, and a polyurethane yarn composed thereof is liable to break when clothing made thereof is worn or the clothing (such as a swim suit) becomes heavy when it absorbs water to deteriorate the comfort as well as worsen the color fastness to rubbing in a wet condition. Also, according to the knowledge of the present inventors, as stated later, a fiber large in water absorption ratio is not always a fiber high in moisture-releasing ability.
Kokai No. 5-271432 discloses that the moisture-permeability is improved and the curling of the fabric is minimized by using a compound in which magnesium salt is dissolved in polyurethane polymer. However, a polyurethane article thus obtained is significantly reduced in mechanical strength when it absorbs moisture, and the moisture is difficult to release once it is absorbed, whereby the comfort is hardly improved when the wearer sweats, and a high color fastness is not obtained.
An object of the present invention is to provide a high elongation and high stretch-recovery synthetic fiber which is low in strength deterioration when moistened and improved in moisture releasing property, and a fabric made of such a fiber. A more concrete object of the present invention is to provide a high elongation and high stretch-recovery synthetic fiber suitable for producing a fabric for clothing use, maintaining a good processability during a wet treatment such as a dyeing process, which fiber is free from stuffiness and rich in stretchability to result in an excellent wearing comfort, and a fabric using such a fiber.